Matteo Renzi should not resign if he loses the referendum on which he has staked his premiership — but if he does it will not be a disaster, his predecessor as Italy's prime minister told CNBC on Friday.

Italians will vote in October on constitutional reforms championed by Renzi, which include plans to strip the Italian Senate of much of its power.

Mario Monti, the economist who led an Italian technocrat government between 2011 and 2013, said Renzi could win the vote — and that promising to resign if he did not was misguided.

"I think that was ill-advised on his part and you will notice he is now pouring a lot of water into that wine, which for a Tuscan is not so natural, probably," Monti told CNBC at the Ambrosetti Forum on economics in Italy.

The size of the reforms touted and Renzi's promise to resign if the referendum fails has led to comparisons with the U.K.'s vote to leave the European Union back in June. The U.K.'s Prime Minister, David Cameron, campaigned for the public to vote "remain" — and resigned after they voted to leave instead.

Monti played down the Brexit vote comparison on Friday.

"I think the international media are a bit misled when they focus so much on Italy now, sort of believing … this would be an earthquake similar to what Brexit may have over time. I am personally sure this will not be the case … It is a bit overdoing the case to say the whole European economy would be shaken," he told CNBC.

Monti denied Italy was "ungovernable" without constitutional reform and said that Renzi's proposed changes to the Senate should go further.

"I think it would have been preferable to eliminate the Senate all together, rather than filing a new Senate with representatives of the regional political class, which has not given the best performance in recent years in Italy, including in terms of honesty," he told CNBC.